FIG. 5 is a vertical sectional view of a general twin clutch, FIG. 6 is a partially fragmental side view viewed in a direction of arrow VI of FIG. 5, and FIG. 7 is a bottom view viewed in a direction of arrow VII of FIG. 6. In FIG. 5, a twin clutch 1 is disposed between an input side flywheel 2 and an output side clutch shaft (center line 3). The flywheel 2 is fastened to a crank shaft end by plural bolts 4, and a spacer (flywheel ring) 5 forming an outer shell of the twin clutch 1 and a clutch cover 6 are fastened by common bolt 7 to an outer peripheral part of the flywheel 2. In the twin clutch 1; a first clutch disc 8, an intermediate plate 9, a second clutch disc 11 and a pressure plate 12 are disposed successively form the flywheel 2 side. The first and second clutch discs 8 & 11 spline fit onto the clutch shaft 3 (an input shaft of transmission) at their central hub portions. The intermediate plate 9 is coupled to the spacer 5 through a strap 13 extending in a circumferential direction, and the pressure plate 12 is coupled to the clutch cover 6 through a strap 14 (FIG. 6) extending samely in the circumferential direction. Plural clutch springs 16 are compressively installed between the pressure plate 12 and the clutch cover 6, and at the same time release levers 17 for disengaging the clutch are assembled radially. The release lever 17 is supported by the clutch cover 6 through a pin 18 and a lever support 19, and at the same time connected to a projection 21 of the pressure plate 12 through the pin 20. A spring force of the clutch spring 16 causes a facing 22 at an outer periphery of the first clutch disc 8 to be held between the flywheel 2 and the intermediate plate 9, and it causes a facing 23 of the second clutch disc 11 to be held between the intermediate plate 9 and the pressure plate 12.
When a clutch pedal (not shown) is operated to push forth the release lever 17 to a position 17' in a clutch disengaging process, the pressure plate 12 is moved backward by a lever action of the release lever 17 to a right side of FIG. 5 against the spring force of the clutch spring 16, so that the facing 23 is released. And at the same time, the intermediate plate 9 is moved backward by a spring force of the strap 13 to the right side of FIG. 5 to an amount restricted by an intermediate plate positioning mechanism described later, so that the facing 22 is released.
A conventional intermediate plate positioning mechanism will be described hereunder. Conventionally, as illustrated in FIG. 7, a stopper pin 25 is press fitted in a hole 27 of a boss 26 at an outer periphery of the intermediate plate 9, one end of the stopper pin 25 faces on the flywheel 2 and the other end thereof faces on the spacer 5, and a length of the stopper pin 25 is so defined that a specified clearance L1 is made between the stopper pin 25 and the spacer 5 at the time when the clutch is engaged as shown by FIG. 7. The stopper pin 25 is a so-called split pin which is made of a rectangular spring steel plate formed into a cylindrical shape so that a slit 28 extending in its longitudinal direction may be formed even when the pin is press fitted in the hole 27.
When the facing 23 is moved backward in a left upper side of FIG. 7 in the clutch disengaging process, the intermediate plate 9 is moved backward by the spring force of the strap 13 in the same direction to an amount of the clearance L1 (disengagement allowance) so as to release the facing 22. When the facing 22 is worn out, the intermediate plate 9 slides on the stopper pin 25 at a part of the hole 27 in a right lower side of FIG. 7 at the time of clutch engagement where the intermediate plate 9 moves forward in the right lower direction of FIG. 7. Consequently, the intermediate plate 9 is able to give a specified load on the facing 22 and at the same time to provide the specified disengagement allowance through the backward motion of the clearance L1 when disengaging the clutch. Thus, the specified disengagement allowance can always be secured in relation to the facing 22.
According to the above-mentioned conventional structure, however, the stopper pin 25 is affected by heat to cause an instability of load (sliding resistance) at time of the stopper pin 25 sliding relatively to the hole 27 so that a pressing force by which the intermediate plate 9 presses the facing 22 on the flywheel 2 fluctuates to an extent of said instable load. Namely, since the hole 27 in which the stopper pin 25 fits is made on the outer peripheral boss 26 of the intermediate plate 9 having friction surfaces with the facings 22 & 23 on both sides thereof, friction heat is transmitted directly to the hole 27 and the stopper pin 25 so that fluctuation of outside diameters of the hole 27 and the stopper pin 25 and deterioration of spring characteristic of the stopper pin 25 etc. due to the heat become inevitable. Therefore, the foregoing trouble will naturally arise.
The present invention has an object to solve the above-mentioned conventional problem by thermally isolating the spring member from the intermediate plate which is apt to acuire a high temperature during operation and at the same time by employing as the spring member a coned disc spring developing a less load change in relation to a deflection change.